In recent years, there has been a strong demand for a high power output semiconductor laser for a light source used in devices of information processing such as an optical disk memory device. However, there is an obstacle for realizing a high power output in the semiconductor laser, namely Catastrophic Optical Damage (defined as "COD" hereinafter) which occurs at a facet of the semiconductor laser. COD occurs when the semiconductor laser facet is heated and damaged partially by absorbing the laser light at the facet.
A first conventional semiconductor laser is described on pages 383 to 384, Electronics Letters, 1984, vol. 20. The first conventional semiconductor laser has a multi-quantum well (defined as "MQW" hereinafter) active layer. MQW is also called as "artificial super-lattices". In the semiconductor laser, MQW of the active layer in the vicinity of the semiconductor laser facet is disordered by selectively diffused impurity, so that the bandgap energy of MQW of the active layer in the vicinity of the facet is larger than that in the inner part of the laser resonator of the semiconductor laser. As a result, the semiconductor laser facet becomes hard to absorb the laser light, so that COD is reduced in the semiconductor laser. The disorder of MQW is described on pages 776 to 778, Applied Physics Letters, 1981, vol. 38. In the semiconductor laser, some part of a p-type cladding layer and an electrode of the semiconductor laser is removed in order to prevent an injection of currents into the active layer, for the reason that there are many defects of the crystal lattice of the active layer in the vicinity of the facet because of the high density impurity diffusion, so that the injection of current may cause destruction of the active layer.
A second conventional semiconductor laser is described in Japanese Patent Publication No. 64-14986. The second conventional semiconductor laser has a natural super-lattice active layer. The natural super-lattices are disordered by selective impurity diffusion in the vicinities of both facets of the semiconductor laser, so that the bandgap energy becomes large in comparison with that of the natural super-lattices before being disordered. It is known that the natural super-lattices are formed in the growth of GaInP or AlGaInP by Metalorganic Vapor Phase Epitaxy method (defined as "MOVPE method" hereinafter), and that Al (or Ga) and In atoms are in a row mutually in a direction of (1 1 1) in the natural super-lattices. The formation of the super-lattices is thought to be caused by differences of bonding lengths of Al-P, Ga-P and In-P in AlGaInP, for instance. It is described on pages L1549 to L1552, Japanese Journal of Applied Physics, 1988, vol. 27 that the natural super-lattices are disordered by impurity diffusion in order to increase the bandgap energy, as like in the case of MQW.
According to the first and second conventional semiconductor lasers, however, there is a disadvantage in that there are many defects of the crystal lattice of the active layer in the vicinity of the facet because of the high density impurity diffusion, so that the injection of current may cause destruction of the active layer. In the first conventional semiconductor laser, some part of a p-type cladding layer and an electrode of the semiconductor laser is removed to prevent the injection of current into the active layer, however, there is another disadvantage in that the active layer of the semiconductor laser may be suffered by the strain stress during the process of attaching the semiconductor laser to a heatsink because of lack of the cladding layer as a protection layer, so that the reliability of the semiconductor laser may reduce.